1. Field of the Invention
This invention relates to the field of ceramic base structural materials which are useful at temperatures approaching 2700.degree. F.
2. Description of the Prior Art
As shown in the patent to Kraft U.S. Pat. No. 3,124,452, it is now known that various eutectic compositions may, by directional solidification techniques, be cast into bodies displaying unique ordered microstructures and properties. With the metallic eutectics or eutectic-type allows a number of particularly useful systems have been developed to take advantage of the ordered eutectic alloy microstructures in gas turbine engine hardware, including the aligned nickel-base alloys described in the patent to Thompson U.S. Pat. No. 3,554,817 and the aligned cobalt-base alloys of monovariant eutectic composition of Thompson et al U.S. Pat. No. 3,564,940. Also of substantial utility are the skeletal or cellular microstructures mentioned in Lemkey et al U.S. Pat. No. 3,552,953.
The metallic alloys are, however, typically limited in terms of their practical operating temperatures. To satisfy the increasing demand for gas turbine engine materials which will be strong at very high temperatures, attention has quite naturally been given to ceramics which, from the standpoint of their high temperature capabilities, easily surpass most metallic materials. However, the moderate temperature capabilities of the bulk of the ceramics are generally so low that they are not usable in many important applications for which they might otherwise be well suited although some strides have been made leading to property improvements sufficient for use in some applications as discussed, for example, in the patent to Marshall et al U.S. Pat. No. 3,181,939.
U.S. Pat. No. 3,761,295 depicts a ceramic-ceramic eutectic system which possesses useful properties when directionally solidified. A group of ceramic-metallic eutectic systems are described in U.S. Pat. No. 3,796,673, and appear to have application for certain electronic applications.